The extinction of prehistoric megafauna such as the woolly mammoth, cave lion, and woolly rhinoceros at the end of the last ice age is often attributed to the spread of early humans throughout the globe. Although congestion led to the extinction of some species, a study that appeared on August 13 in the journal Current biology found that the extinction of the woolly rhino may have had another cause: climate change. Listing the ancient DNA from 14 of these megaherbivores, the researchers found that the rhinoceros wool population remained stable and diverse until just a few thousand years before it disappeared from Siberia, when temperatures likely rose sharply for the species. adapted from the cold.
“It was originally thought that humans appeared in north-eastern Siberia fourteen or fifteen thousand years ago, around the time woolly rhinos disappeared. But recently, there have been some discoveries of the oldest places of human occupation, the most famous of which is about thirty thousand years old, “says senior author Love Dalén, professor of evolutionary genetics at the Center for Palaeogenetics, a joint venture between Stockholm University and the Swedish Museum of Natural History. “So the decline toward woolly rhinoceros extinction does not coincide so much with the first appearance of humans in the region. If anything, we actually see something that looks a bit like an increase in population size during this period.”
To learn about the size and viability of the rhino wool population in Siberia, the researchers studied DNA from tissue, bone and hair samples of 14 individuals. “We sequenced a complete nuclear genome to look at time and estimate population sizes, and we also listed fourteen mitochondrial genomes to estimate the effective sizes of the female population,” says first author Edana Lord, Ph.D. student at the Center for Paleeogenetics.
By looking at the heterozygosity, or genetic diversity, of these genomes, researchers were able to estimate the wool root population for tens of thousands of years before their extinction. “We looked at changes in population size and assessed inbreeding,” says co-author Nicolas Dussex, a postdoctoral fellow at the Center for Paleeogenetics. “We found that after an increase in population size at the beginning of a cold period about 29,000 years ago, the wool root population size remained constant and that at this time, inbreeding was low.”
This stability lasted until people began to live in Siberia, resisting the declines that would be expected if wool rhinos disappeared due to hunting. “That’s the interesting thing,” says Lord. “We do not really see a decrease in population size after 29,000 years ago. The data we just looked at goes back to 18,500 years ago, which is roughly 4,500 years before they disappeared, so that means they fell somewhere in that gap. “
DNA data also revealed genetic mutations that helped woolly rhinos adapt to colder weather. One of these mutations, a type of receptor on the skin for feeling hot and cold temperatures, has also been found in wool moms. Adjustments like this suggest the wool rhinoceros, which was particularly suitable for the frozen climate of north-eastern Siberia, may have fallen due to the heat of a short heating period, known as the interstadial Bølling-Allerød, which coincided with their disappearance towards the end of the last ice age.
“We are moving away from the idea of people taking over everything as soon as they come to an environment, and instead we will clarify the role of climate in megafaunal extinctions,” says Lord. “Although we cannot rule out human involvement, we suggest that the extinction of the woolly rosoceros was more likely for the climate.”
The researchers hope to study the DNA of additional fur rhinoceroses that lived in that significant 4,500-year gap between the last genome they listed and their extinction. “What we want to do now is try to get more rhino genome sequences that are between eighteen and fourteen thousand years old, because at some point, they certainly have to fall,” says Dalén. Researchers are also looking at other megafauna adapted from the cold to see what further effects the volatile, unstable climate had. “We know the climate has changed a lot, but the question is: how many different animals were affected and what do they have in common?”
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Current biology, Lord et al .: “Demographic stability before extinction and genomic signatures of adaptation in woolly rhinos” www.cell.com/current-biology/f… 0960-9822 (20) 31071-X, DOI: 10.1016 / j. cub.2020.07.046
citation: Ancient genomes suggest that wool rhinos disappear due to climate change, not overload (2020, August 13) taken August 13, 2020 by https://phys.org/news/2020-08-ancient-genomes -woolly-rhinos-extinct. html
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